1. Field of the Invention
The present invention relates to a twin-screw extruder used to extrusion molding of a honeycomb formed body and the like.
2. Description of the Related Art
A honeycomb-like structure (honeycomb structure) is widely used as a carrier for purifying exhaust gases from various internal combustion engines such automobile engines, a catalyst carrier for deodorization, a filter for various filtering equipment, a heat exchanger unit, and a carrier for a chemical reaction equipment such as a catalyst carrier of a reforming catalyst of a fuel cell battery, and the like. Ordinarily, the honeycomb structure is manufactured by obtaining a formed body (honeycomb formed body) having a predetermined honeycomb structure by extrusion molding clay composed of a ceramic material and the like and drying and baking the formed body.
Conventionally, a twin-screw extruder 21 having a structure as shown in FIG. 4 is widely used as an apparatus for obtaining the honeycomb, formed body. The twin-screw extruder 21 has two screws 7 disposed in parallel in the inside thereof and further includes a barrel 2 having an opening 3 to an end and a extrusion molding die 9 disposed to the opening 3 side of the barrel 2 through a straightening vane 22 and a filter net 8. FIG. 5A and FIG. 5B are a front elevational view of the straightening vane 22 and a sectional view thereof in a thickness direction. As shown in these figures, the straightening vane 22 has one through hole 23 formed thereto, and the through hole 23 acts as a flow path of the clay extruded from the opening 3 of the barrel 2. The through hole 23 is ordinarily a circular hole having a diameter of about 8 to 36 mm (note that no prior art document is found as to a technology relating to the straightening vane structure). The filter net (screen) 8 is used to remove coarse grains and foreign substances in the clay and disposed upstream of the die 9 in the flow direction of the clay. The die 9 has slits formed thereto corresponding to the sizes of the through holes and the partitions of a honeycomb formed body to be obtained.
A forming material charged into the inside of the barrel 2 through a material charge hopper 10 which is communicating inside of the barrel 2 with outside of the barrel 2 is knead by the two screws 7 driven by a driving unit 11 composed of a motor, a gear box, and the like while being applied with shear force. Thereafter, the forming material is continuously extruded to the outside of the barrel 2 as clay from the opening 3 disposed to the end of the barrel 2. Thus extruded clay flows into the through hole 23 of the straightening vane 22 disposed in intimate contact with the opening 3 of the barrel 2, extruded from the side edge of the through hole 23 on the outlet side thereof into a space 15 between the straightening vane 22 and the filter net 8. After the inside of the space 15 is approximately filled with the clay, the clay passes through the filter net 8, moves into a space 16 between the filter net 8 and the die 9. After the inside of the space 16 is approximately filled with the clay, it is forced into the slits formed to the die 9 from the edge face of the die 9 on the inlet side thereof and extruded from the edge face of the die 9 on the outlet side thereof while being formed to a predetermined shape.
Incidentally, in conventional twin-screw extruder, when the amount of extrusion per unit time of the formed body (the amount of clay supplied to the die) changes, the formed body is liable to be deformed. As a result, a formed body must be made by extruding a constant amount of clay at all times, and thus it is difficult to carry out production by appropriately flexibly changing the amount to clay to be extruded.
An object of the present invention, which was made in view of the conventional circumstances, is to provide a twin-screw extruder for manufacturing a formed body which is unlike to be deformed even if the amount of the formed body to be extruded per unit time changes.